In general, polyolefin resins are relatively inexpensive, have excellent performances such as chemical resistance, water resistance, and heat resistance, and are used in a wide range of fields as materials for automotive parts, electrical parts, building materials, food packages, etc. Although polyolefin resins have such features, it is difficult to coat or bond the resins because the resins are crystalline and nonpolar.
For the coating or bonding of such poorly bondable polyolefin resins, lowly chlorinated polyolefins showing high adhesion to polyolefin resins have been used as binder resins. A chlorinated isotactic polypropylene chlorinated to 20 to 40% by weight has been proposed as a binder resin for printing inks for polypropylene films (see, for example, patent document 1). A chlorinated propylene/ethylene copolymer chlorinated to 20 to 40% by weight has been proposed as a binder resin for printing inks or adhesives for polyolefins (see, for example, patent documents 2 and 3).
Furthermore, a lowly chlorinated propylene/α-olefin copolymer having a chlorine content of 5 to 50% by weight and containing a carboxylic acid and/or carboxylic acid anhydride has been proposed as a primer for the coating of polyolefin moldings or as a binder resin for the coating (see, for example, patent documents 4 and 5).
In general, the higher the chlorine contents of those chlorinated polyolefins becomes, the more the adhesion to polyolefins and the solvent resistance of the chlorinated polyolefins tend to become poor. It is therefore desirable to set the chlorine content at a value as low as possible. However, too low chlorine contents result in a poor solution state to cause a viscosity increase or gelation during storage. Such a chlorinated polyolefin hence considerably impairs workability, such as applicability by, e.g., spraying. Further, even when a lowly chlorinated polyolefin is regulated so as to have a chlorine content in a range where workability such as applicability by, e.g., spraying is not impaired, a solution of this chlorinated polyolefin, when stored at a low temperature, comes to have poor flowability and considerable limitations are imposed on the handling of the solution at low temperature in winter. Although reducing the concentration of such a lowly chlorinated polyolefin in solutions can improve low-temperature flowability, low concentrations result in difficulties in dispersing a pigment when an ink or coating material is prepared from the solution. Furthermore, low concentrations pose problems, for example, that transportation cost increases.
For mitigating such problems, a binder resin solution obtained by dissolving a lowly chlorinated polyolefin in a mixed solvent of an alicyclic hydrocarbon and an aromatic hydrocarbon has been proposed as a solution showing satisfactory low-temperature flowability (see, for example, patent document 6).
However, use of such a mixed solvent has a drawback that it necessitates a step in production to cause a cost increase. Furthermore, in case where that solution is used, for example, as part of a primer ingredient for coating and mixed with a dispersed resin, low-temperature flowability becomes poor because of the resultant change in solvent composition, etc. It is therefore difficult to consider that the binder resin solution is a fundamental resolution.    Patent Document 1 JP-B-46-27489    Patent Document 2 JP-B-50-35445    Patent Document 3 JP-B-50-37688    Patent Document 4 JP-B-63-50381    Patent Document 5 JP-B-63-36624    Patent Document 6 JP-A-6-306227